[meteorite-list] LL7 Chondrites

From: David Weir <dgweir_at_meteoritecentral.com>
Date: Thu Apr 22 10:32:54 2004
Message-ID: <40636720.D9C0F939_at_earthlink.net>

Hey Adam,

Yes, I agree with you. Very perceptive. The two types are mutually
exclusive based on the definition of Dodd. Type 7 ordinary chondrites
were originally defined by Dodd et al. (1975) according to specific
petrographic characteristics. They listed three metamorphic criteria to
distinguish between petrographic types 6 and 7:

1.the presence of poorly defined chondrules in type 6, but only relict
chondrules in type 7

2.low-Ca pyroxenes in type 6 contain no more than 1.0 wt% CaO (1.0 wt% =
~1.9 mol% Wo), but more than 1.0 wt% in type 7; conversely, the CaO
content of high-Ca pyroxenes decreases from type 6 to type 7

3.feldspar grains gradually coarsen to reach a size of at least 0.1 mm
in type 7

Perhaps this is one of those confused cases of classification in which
different labs call things by different terminology. Could they have
found both petrographic phases in the stone and used the slash to
indicate this? Who did the classification?

Regards,
David
Received on Thu 25 Mar 2004 06:11:28 PM PST